1. Field of the Invention
The present invention-relates to a video signal recording and reproducing apparatus for recording a video signal of a wide band on a magnetic tape such as a hi-vision video tape recorder (hereinafter referred to as the hi-vision VTR), and a method of recording and reproducing a video signal and, more particularly, to a VTR for recording a component signal, called a base band VTR.
2. Description of the Background Art
With recent development of image techniques, a test broadcasting of a hi-vision television signal has been started, and a real broadcasting is about to start in the very near future. Under such circumstances, a hi-vision VTR for recording and reproducing a video signal of the hi-vision broadcasting has also started to be put in the market place.
FIG. 9A is a block diagram showing a background art example of such a hi-vision VTR. In FIG. 9A, a symbol MT denotes a magnetic tape as a recording medium. This VTR includes a recording system and a reproduction system. The recording system includes A/D converters 1, 2 and 3 for converting a luminance signal Y and color difference signals P.sub.B and P.sub.R from an analog signal to digital data (hereinafter referred to as A/D-converting), a vertical filter and line-sequentially processing circuit 4 for line-sequentially processing digitized color difference signals P.sub.B and P.sub.R and converting the signals into one data P.sub.B /P.sub.R, and a shuffling circuit 37 for dividing A/D-converted luminance data Y and color difference data P.sub.B /P.sub.R into data of channels CHA and CHB. This recording system further includes corresponding to the channels CHA and CHB, D/A converters 6 and 7, FM modulators 8 and 9, recording amplifiers 10 and 11, and magnetic head pairs 54 and 55.
The reproduction system includes corresponding to the channels CHA and CHB, reproduction amplifiers 14 and 15, FM demodulators 16 and 17, A/D converters 18 and 19, and time base correctors 38 and 39 for carrying out a time base correction. The reproducing system further includes a deshuffling circuit 40 for separating time-base corrected signals of the channels CHA and CHB into luminance data Y and color difference data P.sub.B /P.sub.R (i.e., carrying out an opposite operation to that of the shuffling circuit 37), an interpolation filter 25, and D/A converters 26, 27 and 28.
In a recording operation, the luminance signal Y and the color difference signals P.sub.B and P.sub.R included in an input video signal are input to the A/D converters 1, 2 and 3, respectively, and then converted into digital data. A sampling frequency is approximately 44 MHz for the luminance signal Y, while it is approximately 11 MHz for the color difference signals P.sub.B and P.sub.R. The A/D-converted luminance data Y is input intactly to the shuffling circuit 37. The color difference data P.sub.B and P.sub.R, folding noises of which are first removed by the vertical filter are then processed line sequentially by the line sequential processing circuit. The line sequentially processed data are then converted into one data P.sub.B /P.sub.R. The signal P.sub.B /P.sub.R is input to the shuffling circuit 37. The shuffling circuit 37 time-divides the luminance data Y and the color difference data P.sub.B /P.sub.R, then integrates the time-divided luminance data Y and color difference data P.sub.B and P.sub.R, adds data of a negative polarity synchronizing signal and a burst signal to the integrated signal and generates two data of channels CHA and CHB. The details of the shuffling circuit 37 will be described later. The data of channels CHA and CHB are converted into analog signals by the D/A converters 6 and 7, respectively. The respective analog signals are FM-modulated by the respective FM modulators 8 and 9, then current-amplified by the respective recording amplifiers 10 and 11 and applied to the respective magnetic head pairs 54 and 55. The magnetic head pairs 54 and 55 record the amplified signals on a magnetic tape not shown. In practice, the magnetic head pair 54 includes two heads, magnetic heads A1 and A2 opposing by 180.degree.. The magnetic head pair 55 similarly includes two heads, magnetic heads B1 and B2 (see FIG. 14 which will be referred to later.)
In a reproduction operation, the signal of channel CHA reproduced at the magnetic head pair 54 is amplified by the reproduction amplifier 14, while the signal of channel CHB reproduced at the magnetic head pair 55 is amplified by the reproduction amplifier 15. The amplified signals of channels CHA and CHB are input, respectively, to the FM demodulators 16 and 17, in which the signals are demodulated and a dropout is detected. The demodulated signals of channels CHA and CHB are converted into digital data by the A/D converters 18 and 19, respectively, and then input to the time base correctors 38 and 39, respectively. The time base correctors 38 and 39 correct a time base change of the input signals due to jitter or the like and also make a compensation of the dropout detected by the FM demodulators 16 and 17. After that, the time base correctors 38 and 39 output the data of channels CHA and CHB to the deshuffling circuit 40. The deshuffling circuit 40 carries out an opposite processing to that of the shuffling circuit 37. That is, the deshuffling circuit 40 removes data of the negative polarity synchronizing signal and the burst signal and separates the luminance data Y and the color difference data P.sub.B /P.sub.R from the time base multiplexed data of channels CHA and CHB. The luminance data Y restored to the original by the deshuffling circuit 40 is converted into an analog signal by the D/A converter 26 and then output to a monitor or the like not shown. The line sequentially processed color difference data P.sub.B /P.sub.R is alternately interpolated for each line by the interpolation filter 25 and divided into color difference data P.sub.B and P.sub.R. These color difference signals P.sub.B and P.sub.R are converted into analog signals by the D/A converters 27 and 28, respectively, and then output to a monitor or the like not shown similarly to the aforementioned luminance signal Y.
FIG. 9B is a block diagram of the vertical filter and line sequential processing circuit 4 shown in FIG. 9A. With reference to FIG. 9B, the vertical filter and line sequential processing circuit 4 includes vertical filters 4A and 4B which are provided corresponding to color difference data P.sub.B and P.sub.R to remove any interferences caused by folding of the color difference data P.sub.B and P.sub.R, and a switch circuit 6a for alternately selecting an input signal for each 1H.
The vertical filter 4A includes 1H delays 4a and 4b, adders 4c and 4f, and multipliers 4d and 4e. The vertical filter 4B includes 1H relates 5a and 5b, adders 5c and 5f, and multipliers 5d and 5e.
The switch circuit 6a has two input nodes and one output node. One of the input nodes is connected to an output of the adder 4f, the other input node is connected to an output of the adder 5f and the output node is connected to an input of the shuffling circuit 37.
In operation, undelayed color difference data P.sub.B and color difference data which is 2H delayed by the 1H delays 4a and 4b are added together by the adder 4c. The result of addition is attenuated to a 1/4 level by the multiplier 4d. The color difference data P.sub.B which is 1H delayed by the 1H delay 4a is first attenuated to a 1/2 level by the multiplier 4e and then applied to the adder 4f. The adder 4f adds outputs of the multipliers 4d and 4e. The interferences caused by folding of the color difference data P.sub.B are thus removed. The vertical filter 4B removes interferences caused by folding of color difference data P.sub.R similarly to the vertical filter 4A. Consequently, the color difference data P.sub.B and P.sub.R that have passed the vertical filters 4A and 4B are 1H delayed from the luminance data Y. The color difference data P.sub.B and P.sub.R that have passed the vertical filters 4A and 4B are alternately selected by the switch circuit 6a and converted into one color difference data P.sub.B /P.sub.R.
The shuffling processing will now be described. FIG. 10 is a block diagram showing structure of a general shuffling circuit. This shuffling circuit 37 includes switch circuits 41 and 42, field memories 43 and 44, memory controllers 45 and 46, output switch circuits 47a and 47b, and ROMs 48 and 49 for generating a synchronizing signal and a burst signal. Each of the switch circuits 41 and 42 has two input terminals and one output terminal. One of the input terminals is supplied with luminance data Y, and the other input terminal is supplied with color difference data P.sub.B /P.sub.R. The output terminal of the switch circuit 41 is connected to an input of the field memory 43, while the output terminal of the switch circuit 42 is connected to an input of the field memory 44. The field memory 43 includes two memories 43a and 43b for each storing a 1/2 field. During the period that one memory 43a is brought into a write state, the other memory 43b is brought into a read state. The field memory 44 includes two memories 44a and 44b similarly to the field memory 43. The memory controller 45 controls writing and reading of the field memory 43 and also controls addresses. The memory controller 46 controls writing and reading of the field memory 44 and also controls addresses. Further, the memory controllers 45 and 46 control reading of the sync and burst generating ROMs 48 and 49.
In operation, the luminance data Y and the color difference data P.sub.B /P.sub.R input to the shuffling circuit 37 are input to the switch circuits 41 and 42. The switch circuits 41 and 42 alternately switch the input data for each one horizontal period (hereinafter referred to as 1H) and output the switched input data to the field memories 43 and 44 at the succeeding stage. Thus, when an output of the switch circuit 41 is the luminance data Y, for example, an output of the switch circuit 42 is the color difference data P.sub.B /P.sub.R. Video data of one field from the switch circuits 41 and 42 is stored into one memory of each of the field memories 43 and 44, i.e., memories 43a and 44a. Subsequent video data of one field is stored into the other memory of each of the field memories 43 and 44, i.e., memories 43b and 44b. At the same time, the data stored in advance into one memory of each of the field memories 43 and 44 are read. This state is alternately repeated. The video data read from the field memories 43 and 44 and the sync and burst data read from the sync and burst generating ROMs 48 and 49 are appropriately switched by the switch circuits 47a and 47b, respectively, and then output as data of channels CHA and CHB.
FIG. 11 shows mapping of the field memories 43 and 44. A description will now be made with reference to FIG. 11 as to how the video data comprised of the luminance data Y and the color difference data P.sub.B /P.sub.R is specifically time-divided and integrated in the background art example. FIG. 11 merely illustrates video data of one field. Referring to FIG. 11, a CHA memory corresponds to one of the two memories 43a and 43b of the field memory 43, while a CHB memory corresponds to one of the two memories 44a and 44b of the field memory 44. Each 1/2 field memory is divided into two segments, a first segment and a second segment. Data shown on the left part of FIG. 11 are luminance data Y and color difference data P.sub.B /P.sub.R to be input to the switch circuits 41 and 42. The color difference data P.sub.B /P.sub.R is advanced by 1H from the luminance data Y. With two types of data thus input, color difference data P.sub.R 1 is written in a predetermined location (address) of the first segment of the CHA memory during the first 1H. During the next 1H, color difference data P.sub.B 2 is written in a predetermined location of the first segment of the CHB memory, and at the same time, luminance data Y1 is written in the next location of the color difference data P.sub.R 1 of the CHA memory. In this manner, a new 1H of the CHA memory which is time-base multiplexed video data (P.sub.R 1, Y1) can be provided. Further, during the next 1H, color difference data P.sub.R 3 is written in a predetermined location of the second segment of the CHA memory and, at the same time, luminance data Y2 is written in the next location of the color difference data P.sub.B 2 of the CHB memory. In this manner, a new 1H of the CHB memory which is time-base multiplexed video data (P.sub.B 2, Y2) can be provided. Further, during the next 1H, color difference data P.sub.B 4 is written in a predetermined location of the second segment of the CHB memory, and at the same time, luminance data Y3 is written in the next location of the color difference data P.sub.R 3. With each data alternately written into the CHA memory and the CHB memory and in the first and second segments, the shuffling is completed.
As described above, in the background art example, only color difference signals P.sub.R and only luminance signals of odd H are stored in the CHA memory. Data thus recorded are thinned out to two segments of the first and second segments. Data of the same segment of the channels CHA and CHB are read simultaneously and read in the order of the first segment and the second segment.
In order to carry out such shuffling, there must be a time difference of odd H between the luminance data Y and the color difference data P.sub.B /P.sub.R input to the shuffling circuit 37. This is because it is possible to write different data into one memory at a time.
While the color difference data P.sub.B /P.sub.R is advanced by 1H from the luminance data Y in the example shown in FIG. 11, the same processing as above is available even if the color difference data is advanced by 3H from the luminance data, or even if the luminance data is advanced by 1H or 3H from the color difference data. In practice, as shown in FIG. 9B, it is common that a color difference signal is delayed by 1H from a luminance signal because of a process in which the color difference signal is processed by the vertical filter and line sequential processing circuit 4.
FIG. 12 is a diagram showing an output signal of the first segment output from the D/A converters 6 and 7 shown in FIG. 9A. In FIG. 12, CHA denotes output data of the D/A converter 6, and CHB denotes output data of the D/A converter 7. The D/A converter 6 is alternately supplied with data of the first segment of the channel CHA and data of the second segment of the channel CHA from the shuffling circuit 37. The data of each segment includes a synchronizing signal and a burst signal output by the sync and burst generating ROM 48 (FIG. 10). The D/A converter 7 is alternately supplied with data of the first segment of the channel CHB and data of the second segment of the channel CHB from the shuffling circuit 37. The data of each segment includes a synchronizing signal and a burst signal similar to the D/A converter 6.
FIG. 13 is a diagram showing a relationship between a format of a recording signal of one field to be supplied to magnetic heads and rotation of a drum. FIG. 13 shows a state where the first segment is first output and the second segment is then output. FIG. 14 shows arrangement of magnetic heads on a drum; and FIG. 15 shows a recording pattern provided when recording is made on a magnetic tape by the magnetic heads of FIG. 14. With reference to FIG. 14, magnetic head pairs 54 and 55 are provided at opposing positions by 180.degree. on a rotating drum 100. The magnetic head pair 54 has magnetic heads A1 and B1 which are arranged in proximity and have different azimuth angles. The magnetic head pair 55 has magnetic heads A2 and B2 which are arranged in proximity and have different azimuth angles. The magnetic heads A1 and A2 have the same azimuth angle, while the magnetic heads B1 and B2 have the same azimuth angle.
The first segment of the channel CHA of the recording signal shown in FIG. 13 is recorded on the magnetic tape by the magnetic head A1, while the first segment of the channel CHB is recorded on the magnetic tape by the magnetic head B1. The second segment of the channel CHA is recorded on the magnetic tape by the magnetic head A2, while the second segment of the channel CHB is recorded on the magnetic tape by the magnetic head B2. This phenomenon is represented as a conventional recording pattern in FIG. 15. As shown in FIG. 15, one segment of one channel corresponds to one track. Thus, the tracks are denoted with the same reference characters as those of their corresponding magnetic heads.
In operation, during the first period that the rotating drum 100 rotates through 180.degree., the magnetic heads A1 and B1 trace from the lower right to the upper left of the magnetic tape and the first segment is recorded. During the next rotation off 180.degree., the magnetic heads A2 and B2 record the second segment. That is, with one rotation of the drum 100, a video signal of one field is recorded on four tracks on the magnetic tape. At this time, the magnetic heads A1 and B1 record the signal on adjacent two tracks at a time, and the magnetic heads A2 and B2 record the signal on the tracks A2 and B2 at a time so as to be adjacent to the track B1.
A description will now be made on a dropout compensation in the video signal recording and reproducing apparatus of background art with reference to FIGS. 13 and 16. FIG. 16 is a block diagram of the time base corrector circuits 38 and 39 serving also as dropout compensation circuits, showing two channels. Data of the channel CHA shown in FIG. 16 is output from A/D converter 18, while data of the channel CHB is output from the A/D converter 19. A dropout pulse DOPA is output from the FM demodulator 16, while a dropout pulse DOPB is output from the FM demodulator 17. With reference to FIG. 16, this time base corrector circuit 38 includes a line memory 50 for storing one line of the data of the channel CHA, and a memory controller 52 for controlling the line memory 50. The time base corrector circuit 39 includes a line memory 51 for recording one line of the data of the channel CHB, and a memory controller 53 for controlling the line memory 51.
The time base correcting operation of the time base corrector circuits 38 and 39 will now be described. The data of the channels CHA and CHB are reproduced by the reproduction amplifiers 14 and 15, then demodulated by the FM demodulators 16 and 17, A/D-converted by the A/D converters 18 and 19 and applied to the line memories 50 and 51, respectively. Each data has a time base change due to irregularity of the rotation of the drum or expansion and contraction of the tape; however, those data are written into the line memories 50 and 51 by a clock signal having a time base change generated by a PLL circuit or the like not shown. The written data are read by a clock signal having no time base change. This enables the time base correcting operation, i.e., implementation of the time base correctors. The writing and reading of the line memories 50 and 51 is carried out by the memory controllers 52 and 53.
The dropout compensating operation of the time base corrector circuits 38 and 39 will now be described. When detecting a dropout, the FM demodulator 16 outputs a dropout detecting signal DOPA to the time base corrector 38. The dropout detecting signal DOPA is input to the memory controller 52. The memory controller 52 responds to the dropout detecting signal DOPA to stop the data writing operation of the line memory 50. As a result, previous data remains intact in the line memory 50. Since the memory controller 52 carries out a reading operation normally, the dropout portion is replaced by data of the previous horizontal period H, whereby the dropout compensating operation is completed. For example, assume that there is a dropout in video data (P.sub.R 5, Y5) in FIG. 13. Then, the time base corrector circuit 38 makes a compensation by the data stored during the previous horizontal period H, and hence, this dropout portion is replaced with video data (P.sub.R 1, Y1). While the dropout compensating operation of the channel CHA has been described above, the same dropout compensating operation is applied to the channel CHB.
When there is a dropout in the video data (P.sub.R 5, Y5) of FIG. 13, conventionally, the time base corrector circuit 38 replaces the video data (P.sub.R 5, Y5) with the video data (P.sub.R 1, Y1). However, the video data (P.sub.R 1, Y1) and (P.sub.R 5, Y5) are apart from each other by 4H and are thus less correlated with each other. Data which is most correlative with the video data (P.sub.R 5, Y5) is video data (P.sub.R 3, Y3) or (P.sub.R 7, Y7). However, the video data (P.sub.R 3, Y3) or (P.sub.R 7, Y7) is in the second segment. Thus, if the video data (P.sub.R 5, Y5) is replaced with the video data (P.sub.R 3, Y3) or (P.sub.R 7, Y7), it must be waited until the drum 100 rotates through 180.degree., resulting in the problem that a considerably large memory must be provided in order to hold the data during the rotation of 180.degree..
In addition, in the recording system of background art, only signals P.sub.R of a red type are collected in the color difference signal of the channel CHA, and only signals P.sub.B of a blue type are collected in the color difference signal of the channel CHB as shown in FIG. 13. In this case, if there is a difference in characteristics between a circuit for recording and reproducing on the basis of data of the channel CHA and a circuit for recording and reproducing on the basis of data of the channel CHB, it appears visually that an image has improper or poor hues. This problem occurs often in a VTR with 2 channel recording.